1. Field of the Invention
This invention pertains to electron guns for devices such as cathode ray tubes (CRTs). More particularly, apparatus and method that may use modified parts of conventional electron guns are provided for mounting field emission devices.
2. Description of Related Art
A conventional electron gun uses a thermionic emitter as the source of electrons. FIG. 1 illustrates a common configuration of the lower parts of an electron gun using a thermionic emitter. Parts of an electron gun having a cathode and two grids are generally shown at 10. Both grids, along with other grids, are normally xe2x80x9cbeadedxe2x80x9d into a structure that makes up the entire electron gun. Filament 12 is used to heat emissive coating 14 to cause electron emission. Cathode cap 16, attached to cathode shank 18, supports emissive coating 14 (usually a combination of one or more of barium, strontium or calcium carbonates, which are converted to oxides in a CRT). Cathode shank 18 is normally welded to interface ring 20. Interface ring 20 may be formed integral in ceramic cathode mount 22. Ceramic cathode mount 22 is free to slide in grid 24 but is fastened in place by welding during final electron gun assembly. Grid 24 (G1) and Grid 26 (G2) are used to focus and accelerate the electrons produced by emissive coating 14. The grids are biased electrically in a way to create a source of electrons that can be further focused and modulated by other grids to satisfy CRT requirements.
The technology to allow replacement of cathodes based on thermionic emission with cold cathodes based on field emission of electrons (Field Emission Devices or FEDs) has been developing in recent years. The emission of electrons from cold cathodes may occur from microtips that are fabricated from molybdenum, silicon or, in very recent years, carbon-based materials. It has been demonstrated that the carbon-based material or diamond-like material can be monolithically integrated with gated electrodes in a self-aligned structure, using integrated circuit fabrication techniques (xe2x80x9cAdvanced CVD Diamond Microtip Devices for Extreme Applications,xe2x80x9d MAT. RES. SOC. SYMP. PROC., Vol. 509 (1998)). The use of field emission devices with the extraction gate built-in eliminates the need for two of the electrodes in an electron gun built on thermionic emission, G1 and G2 of FIG. 1 Elimination of these electrodes simplifies the gun and also reduces its length. The application of the integrated carbon-like cathode and electrodes into an electron gun has been described in a pending and commonly assigned patent application entitled xe2x80x9cCompact Field Emission Electron Gun and Focus Lens,xe2x80x9d filed Jul. 19, 1999, Ser. No. 09/356,851, with named inventors Rich Gorski and Keith D. Jamison, which is incorporated herein by reference. A segmented cathode has been disclosed in pending and commonly assigned patent application xe2x80x9cSegmented Gate Drive for Dynamic Beam Correction in Field Emission Cathodes,xe2x80x9d filed Dec. 31, 19999, Ser. No. 09/476,051, with named inventors Keith D. Jamison and Donald E. Patterson, which is incorporated herein by reference. A package structure for mounting a field emitting cathode into an electron gun is described in a pending and commonly assigned patent application entitled xe2x80x9cPackage Structure for Mounting a Field Emitting Device in an Electron Gunxe2x80x9d, filed Jan. 28, 2000, Ser. No. 09/493,379, with named inventors Randolph D. Schueller, Kent R. Kalar and Anthony A. Kloba, which is incorporated herein by reference.
Structures for incorporating field emission cathodes into an electron gun are known. but these structures require either considerable re-engineering or replacement of the parts of electron guns using thermionic emitters or newly designed parts. The electron gun design changes and gun part tool modifications are both costly and time-consuming. The use of field emission devices (FEDs) as cathodes is new in the cathode ray tube (CRT) industry and demonstration of their benefits in a CRT using prior methods or apparatus would require costly and time-consuming electron gun design changes. Once the advantages of FEDs are demonstrated, these changes are expected to prove well worth the expense. What is needed is a structure and method that require minimal modification of the parts of already commercial electron guns that use thermionic emission, i.e., that do not require extensive gun design and part tooling changes, while serving all the requirements of FEDs. Use of the structure in a CRT should also allow minimum changes in electrical connections to the CRT.
An electron gun structure for use of a field emission cathode having an integral extraction grid is provided. The structure includes a spring confined in a hollow member, which may be the grid (G1) of a conventional electron gun, that acts on a shank, which may be the cathode shank of a conventional electron gun, to press an electrical contact area around an emitting array against a second surface, which may be the grid (G2) of a conventional electron gun. The electrical contact area is electrically connected to the extraction grid of a field emission array. The grid may be integrally formed with the emitters of the array. The field emitting array is formed on a substrate and is preferably carbon-based. In another embodiment, a support plate is placed beneath the substrate to increase the mechanical contact area between the cathode cap and the FED substrate. In yet another embodiment, the cathode shank is cut off, which may reduce angular mounting errors in some applications.